Short chain fatty acids (SCFA) are normal products of anaerobic bacterial fermentation of carbohydrates in the colon and are the major energy source for the colonic epithelium. Approximately 90% of the total SCFA content in the colon is composed of acetic, propionic, and n-butyric acids. Cummings, J. H. Lancet (1983) 1:1206-1209; Roediger, W. Gut (1980) 21:793-798; Roediger, W. Gastroenterology (1982) 83:424-429. It has been suggested that a lack of luminal SCFAs leads to mucosal atrophy in the short term and nutritional colitis after prolonged periods. Roediger, W. Dis. Col. and Rectum (1990) 33:858-862. This is particularly evident in diversion colitis which develops after diversion of the fecal stream and resolves with restoration of colorectal continuity. Glotzer et al. Gastroenterology (1981) 80:438-441. SCFA enemas have been shown to be effective in the treatment of diversion colitis. Harig et al. N. Engl. J. Med. (1989) 320:23-28.
It is not known whether or not ulcerative colitis has the same cause as diversion colitis. While some investigators have shown that SCFA levels are decreased in the stool of patients with ulcerative colitis (Vernia et al. Dig. Dis. Sci. (1988) 33:1353-1358) and that mitochondrial fatty acid oxidation is abnormal in colon cells isolated from patients with active disease (Roediger, W. Lancet (1980) 2:712-715), it is not known whether these alterations are responsible for or a result of active ulcerative colitis. The histologic appearance of active ulcerative colitis includes an intense lymphoplasmocytosis limited to the mucosa and submucosa often notable for a neutrophilic infiltrate invading the colonic epithelium, referred to as a crypt abscess. Ulcerative colitis may be, therefore, classified as a disorder of the colonic mucosa. Several investigators have shown that the colonic epithelium is in a hyperproliferative state with the expansion of the proliferative compartment from the lower crypt to the upper crypt extending to the surface epithelium of the colon. Biasco et al. Cancer Res. (1984) 44:5450-5454; Serafini et al. Gut (1981) 22:648-652. This proliferative state is independent of the degree of inflammation as well as the duration of disease and exists even when the disease is in a quiescent state. These findings suggest an intrinsic abnormality of the colonic epithelium in ulcerative colitis. Similar hyperproliferative states have been observed in patients at risk for colonic malignancy such as in familial polyposis coli, sporadic colon adenomas and familial nonpolyposis colon cancer. Risio, M. J. Cell Biochem. (1992) 16G:79-87.
Butyrate enemas have been used to reduce inflammation in patients with distal ulcerative colitis. Breuer et al. Dig. Dis. Sci. (1991) 36:185-187; Scheppach et al. Gastroenterology (1992) 103:51-56; Steinhart et al. Am. J. Gastro. (1994) 89:179-183. In two studies, butyrate enemas were shown to result in a significant clinical response in patients whose disease did not respond to traditional forms of treatment including use of corticosteroids and 5-amino salicylic acid compounds. The basis of this response is unknown. Scheppach et al. observed that the labeling index of clonocytes in the upper crypt of patients with ulcerative colitis fell to that of normal healthy controls after treatment with butyrate enemas. Irrigation of the colon with short chain fatty acids also resulted in improvement in patients with diversion colitis. However, the use of butyrate enemas in these diseases is severely limited due to its extremely strong odor which leads to patients refusing to continue treatment.
Butyric acid has also been shown to induce cytodifferentiation in vitro of a wide variety of neoplastic cells. Chen, Z. and Breitman, T. R. Cancer Research (1994) 54:3494-3499. The potential clinical utility of butyric acid, however, is limited by the apparent difficulty of achieving effective concentrations because of rapid metabolism and short plasma half-life. Results in such studies have been variable. For examples, butyric acid, 500 mg/kg body weight per day, as the sodium salt, was given parenterally to a child with acute myelogenous leukemia and induced partial remission. However, sodium butyrate provided at 1% to 2% in the drinking water enhanced development of colonic neoplasia in 1,2-dimethylhydrazine-initiated rats. In further studies Deschner et al. demonstrated dietary butyrate in the form of tributyrin was non-toxic when fed at the 5% level, allowing for normal weight gain and good health. Cancer Letters (1990) 52:79-82. The dietary butyrate in this study did not enhance colonic neoplasia, however, the tributyrate also did not exert a significant protective effect against chemically induced colonic neoplasia.
Chen and Breitman suggest use of tributyrin as a prodrug for butyric acid either as a sole agent or in combination with other agents, for cytodifferentiation therapy of human leukemia and other malignancies. Cancer Research (1994) 54:3494-3499. Diets high in short chain triglycerides such as triacetin and tributyrin have been demonstrated to enhance colonic mucosal adaptation and significantly increase jejunal mucosal mass as compared with chemically defined diets containing equivalent calories in the form of carbohydrate or medium chain triglycerides in rats with surgically created short-bowel syndrome. Kripke et al. Am. J. Clin. Nutr. (1991) 53:954-62. From these studies it was suggested that short chain triglycerides may be a useful new enteral fuel in patients with short-bowel syndrome or other disorders of fat absorption in which medium chain triglycerides represent the current standard of nutritional care. Such diets have also been suggested for patients with neurological injuries to supply systemic caloric and protein requirements without the adverse effects of conventional high glucose diets. Robertson et al. Stroke (1992) 23:564-568. However, Nudelman et al. examined a number of possible prodrugs for butyric acid in cytodifferentiation experiments including glyceryl tributyrate and did not find tributyrates to increase efficacy. J. Med. Chem. (1992) 35(4):687-694. Glyceryl tributyrate, which is capable of releasing three butyrate units per prodrug molecule and has a lipophilicity similar to methyl butyrate, which was shown to inhibit cell proliferation 90%, was only as active as butyric acid with a maximum inhibition of 35%. This lack of activity of the tributyrate was suggested to be due to lower penetration rates into the cells, slow hydrolysis, or a combination of both factors.
It has now been unexpectedly found that tributyrin can be used therapeutically in the treatment of inflammatory bowel disease.